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Preventing and Eliminating Algae

How to Prevent and Eliminate Green Algae

in a Swimming Pool in Greece and Cyprus

from wikiHow - The How to Manual That You Can Edit

This practical advice applies to any swimming pool that fits in the garden of your home living as an ex-pat in the Greek Islands such as Crete, on Mainland Greece or Cyprus. Problems with green algae? After taking care of the algae look after the landscaping, outdoor buildings, walls fences and decks to maintain an eco-friendly environment, to be pleasing to look at throughout the long hot summer.

Green algae is a common swimming pool problem, which may appear as a greenish growth on the floor and walls of a swimming pool, a green tint to the pool water, or greenish material suspended in the pool water. The only swimming pool chemical that will kill an algae growth is chlorine based swimming pool "shock". Shock is a granular form of highly concentrated chlorine, which quickly raises the chlorine level of the swimming pool water. The elevated chlorine level makes the pool water conditions unlivable for anything organic, and algae quickly dies.


Practical Advice - Steps

  1. Step 1: Brush the walls and floor of the swimming pool to remove as much of the algae as possible. This will greatly reduce the amount of time it takes to kill and clear the algae bloom.
  2. Step 2: Ensure that the pH level is within the range of 7.2 - 7.6. This will ensure that any chlorine added will work more efficiently - high pH levels in particular will impair the efficiency of the chlorine doing its job.With the pool filter system running, add a chlorine based swimming pool shock at the rate of 1 lb. per 7,500 gallons/ 1kg per 50,000 litres (or follow the pool shock manufacturer’s dosage suggestion for killing algae). The pool filter system should continue to run 24 hours a day.
  3. Step 3: If the condition of the swimming pool does not significantly improve after 12-24 hours of filtering, add a second dose of chlorine pool shock at the increased rate. Repeat this process until the algae has been eliminated.
  4. Step 4: Once the algae is dead it will turn a white or grayish color, and it will be suspended in the pool water or settle to the floor. When there is no longer any sign of the color green in your pool, thoroughly vacuum the swimming pool. It is recommended that you vacuum dead alge to waste and not through filter.
  5. Step 5: The pool filter should be backwashed or cleaned to be sure that dead algae is not trapped inside the filter. If the filter is not thoroughly cleaned the algae may quickly return.
  6. Step 6: Test and balance all of the pool chemical levels using the following guidelines. Free Chlorine: 1-3 ppm, pH: 7.2 – 7.6, Alkalinity: 80 – 120 ppm and Calcium Hardness: 200 – 350 ppm.
  7. Step 7: Begin adding an algaecide pool chemical on a weekly basis to prevent algae from returning.

Useful Tips

  • Tip 1: Pay closer attention to the chlorine level of your swimming pool water in the future. Algae and harmful bacteria are almost immediately destroyed by a free chlorine level of 1 ppm or higher. You have experienced an algae problem because you have not properly maintained the chlorine level, and it was allowed to drop below 1 ppm. Test pool water frequently and make any necessary adjustments for a clean, safe and easy to maintain swimming pool.
  • Tip 2: Chlorine pool shock needs to be dissolved in a large bucket of water before it is added to the swimming pool. Always add chemicals to water when dissolving. NEVER add water to chemicals.
  • Tip 3: Monitor your pool filter system closely during this entire process and thoroughly backwash or clean the filter each time the pressure rises 10 psi. above the normal operating pressure. The dead algae that your pool filter collects may quickly dirty the filter, and need to be cleaned out frequently.
  • Tip 4: Phosphate Levels - high levels of phosphates in pool water will result in your pool using much more chlorine than usual. They are also one of the main food sources for algae, therefore it is important to have these levels checked fairly regularly especially if the pool seems to be using more chlorine than usual. I have seen a pool with a particularly bad case use approx. 2.5 times the amount of chlorine that it should have, making it very difficult to maintain.
  • Tip 5: In the winter, invest in a mesh pool cover that will prevent debris from entering your pool, yet allow water to pass through, and keep your pool clean.


  • The swimming pool cannot be used until the green algae is dead, and the chlorine level of the pool water has returned to a safe level of 3 ppm* or less. *ppm= parts per million.

Sources and Citations

This is a re-worked article tailor made for the BritsinCrete audience and living on one of the Greek Islands such as Crete or mainland Greece/Cyprus as an ex-pat. Original Author credits are found at the original wikiHow article on How to Eliminate and Prevent Green Algae in a Swimming Pool. All content on wikiHow can be shared under a Creative Commons license.

Further reading on swimming pools if you plan to rent out your property in Crete to be found on our "Getting a Greek Government approved EOT License" page.

Experiences of foreign residents of Building Swimming Pools in Greece and their comments as well as advice from Brits in Crete.